My dog has MRSA: what does it mean and how to fight the bug (Proceedings)


My dog has MRSA: what does it mean and how to fight the bug (Proceedings)

Aug 01, 2011

Canine pyoderma is a common secondary problem, a leading cause of antibiotic use in dogs, and an often frustrating problem for vets and pet owners alike. Unlike many other types of infections, skin infections are often recurrent. This frequently leads to an ongoing cycle of being on and off of antibiotics. The net result is some dogs get treated very regularly and for long periods of time with antibiotics, and it's not particularly surprising that highly drug-resistant bacteria like methicillin-resistant Staph. pseudintermedius (MRSP) eventually become involved.

Most of the time pyoderma develops in response to some underlying skin disease, such as flea allergy dermatitis, food allergy, atopy, Cushing's disease or hypothyroidism. Identifying and treating a skin infection is one thing. Identifying and treating the reason for the infection is another, and that is arguably the most critical component. Ignoring the underlying cause may not be the end of the world for a single infection, because proper treatment and a susceptible bacterium can result in a successful outcome, but ultimately ignoring the real problem can lead to a difficult-to-treat, resistant infection. Any diagnosis of pyoderma should be accompanied by consideration of the underlying cause.

In dogs the main pathogenic methicillin-resistant staphylococcus is MRSP. MRSP is known to colonize people transiently when shed in large quantities by dogs with pyoderma. After the disease resolves carriage also resolves. Nevertheless, infection with MRSP in people, although not common, has been documented. Relative prevalence of MRSP in humans may be unclear due to morphological similarities between MRSP and MRSA. MRSP is becoming increasingly multi-drug resistant in Europe and the United States. In addition to betalactams, it is frequently resistant to gentamicin, tetracycline, macrolides and lincosamides, and trimethoprim/sulfa.

MRSP may be isolated from healthy individuals with no signs of disease; this is considered "carriage" or "colonization", and is distinguished from "infection", wherein the MRSP is causing signs of disease. As multidrug-resistant bacteria such as MRSP become more common in pets, there are increasing questions about how to manage animals that carry them. Limiting the contact with other animals to reduce the spread of the bacterium certainly appears to make sense. However, we also have to realize that this is now a rather common bacterium, and it doesn't cause infections in the majority of animals that get exposed, and it is very rarely a problem in people. That doesn't mean we should ignore it. Sick and immune-suppressed individuals may be at risk to develop an infection with MRSP, especially in high-risk situations, such as hospitals.